For additional taxonomic information, please refer to Gittenberger et al. (2011).

This species is widespread and common throughout its range. Global level, species-specific population data are limited; however, coral reefs have declined globally and are expected to continue rapidly declining due to increasing severe bleaching conditions under temperature stress caused by climate change as well as a variety of other threats. Our species-specific vulnerability traits analysis indicates this species is moderately susceptible to major threats related to coral reef degradation (e.g., disease and bleaching). We applied two analytical approaches involving two different global coral datasets and the species’ distribution map as proxies to infer population decline. Based on global coral cover monitoring data, this species experienced a suspected decline of <25% over the past three generations, or since 1989. Based on the projected onset of annual severe bleaching (ASB) conditions via both SSP2-4.5 and SSP5-8.5 scenarios of global climate model data, in combination with the species’ depth range, distribution and bleaching vulnerability, this species is suspected to decline by less than 25% over the next three generations, or by 2050. Therefore, this species is listed as Least Concern. The change in status from the previous assessment reflects updated declines calculated from improved data on modelled coral cover loss and projected date of annual severe bleaching, along with improved knowledge of species traits.

This species is distributed from the Andaman and Nicobar Islands, Vietnam (Latypov 2011), northwest, north and eastern Australia, southern Japan, South China Sea, and oceanic West Pacific. It has also been confirmed from West Malaysia, southern Vietnam, and the Paracel and Spratly Islands (Huang et al. 2015). 

The depth range is 1-40 m, but the species primarily occurs from 1-25 m (Turak and DeVantier 2019, L. DeVantier pers. comm. 2024).

This species is common (Veron et al. 2016, DeVantier and Turak 2017). It can be locally rare in areas where ornamental coral collection activities occur due to overexploitation and shifts in size-frequency distributions caused by extractive preferences for smaller polyps (Knittweis and Wolff 2010, Hadi et al. 2020). Significant genetic structuring was found in the Spermonde Archipelago, with genetically distinct populations observed at larger scales as well as varying connectivity patterns between populations (Knittweis et al. 2009).

Species-specific, global level population information is limited. However, coral reefs are experiencing severe global level declines due to increasing water temperatures caused by climate change (Hughes et al. 2018). For the purposes of this Red List assessment, we used species-specific vulnerability traits and two analytical approaches based on two global coral datasets to infer past (GCRMN 2021) and future (UNEP 2020) population trends. 
    
Approach 1: Future population trend
The projected onset of annual severe bleaching (ASB) was applied as a proxy to estimate global level population decline. ASB represents the date at which a coral reef will likely experience severe bleaching conditions annually, and beyond which the species will experience a greater than 80% decline as it is not expected to recover (van Hooidonk et al. 2014). ASB is defined as at least eight Degree Heating Weeks (DHW) occurring over a three-month period within a year, and where a DHW occurs when the sea surface temperature is at least 1°C above the maximum monthly mean (van Hooidonk et al. 2014; 2015). We defined the onset of ASB as corresponding to 80% or more decline, however, this is conservative as other studies have found that coral populations may experience near complete mortality and are unlikely to recover with just two incidences of ASB per decade (Obura et al. 2022).

To calculate ASB for each species we applied spatial data made publicly available via a United Nations Environment Programme report (UNEP 2020) that used the 2019 IPCC CMIP6 global climate models to estimate the projected onset of ASB for the years 2015-2100 on a 27 km x 27 km grid according to the 2018 WCMC-UNEP global coral reef distribution map, which has a resolution to 30 m depth. These data are available via two scenarios of Shared Socioeconomic Pathways (SSP), with SSP5-8.5 representing current global emissions and SSP2-4.5 representing a future reduction in emissions (UNEP 2020). We applied SSP5-8.5 since it follows the precautionary approach recommended by the IUCN Red List methodology and SSP2-4.5 since it represents a more moderate climate change scenario that better tracks current policy projections (Roelfsema et al. 2020, Obura et al. 2022). To acknowledge varying levels of coral adaptation to thermal stress, both of these spatial data layers are available for all quarter degree intervals between 0° and 2°C (UNEP 2020); however, coral adaptation in general is poorly understood and varies by species and locality (van Hooidonk et al. 2013, Logan et al. 2014). To account for adaptation, we calculated two estimates of ASB onset for both the SSP5-8.5 and the SSP2-4.5, where the first estimate assumes the species has no level of adaptation (0°C) and the second assumes a capacity for 1°C of adaptation. We clipped each of these four UNEP (2020) spatial data layers to the species’ distribution and calculated the average year of ASB onset across all overlapping grid cells. 

Based on this spatial analysis, the onset of ASB across this species’ range is projected to occur on average by the year 2035 for SSP5-8.5 and by 2039 for SSP2-4.5 assuming no level of adaptation and by the year 2063 for SSP5-8.5 and by 2071 for SSP2-4.5 assuming 1°C of adaptation. For species where ASB occurs within 3-generation lengths, the 3-generation reduction is calculated as 80% multiplied by two proportions: (i) the proportion of the species' depth range that is in 0–30 m range, and (ii) for widespread species, the proportion of cells within the species' range that are expected to experience ASB under SSP2-4.5 before 2050 (three generation lengths). We inferred that the uncertainty associated with the estimate of population decline based on 1°C of adaptation is lower given this species is primarily restricted to depths shallower than 30 m and is more resilient to bleaching. For widespread species, the final estimate of decline was further adjusted by excluding the proportion of cells within its range that were expected to experience ASB under SSP2-4.5 after 2050 (three generation lengths), in order to account for the potential resilience of species to the asynchronous variability of bleaching events that occur across the Indo-Pacific. The relative vulnerability to bleaching (i.e., highly susceptible, moderately susceptible, or more resilient) is primarily based on scientific species expert knowledge. The application of the species’ depth range as a vulnerability factor is based on the understanding that a coral species with shallow depth preferences is more frequently exposed to extreme temperatures and is expected to decline at a faster global rate than species that also or primarily occur in deeper, cooler waters (Riegl and Piller 2003). Ocean acidification, which is measured by aragonite saturation, is also considered a major threat to corals due to the impacts of climate change, however, the impacts are expected to be more severe in cooler and/or deeper waters (Couce et al. 2013, van Hooidonk et al. 2014, Hoegh-Guldberg et al. 2017). Although the exact threshold of aragonite saturation that is expected to cause significant decline is not well-known, in the Pacific, changes in aragonite saturation are expected to be most severe in high-latitude reefs (van Hooidonk et al. 2014). Therefore, this species is suspected to experience a future global level decline of less than 25% by the year 2050, regardless of the SSP2-4.5 or SSP5-8.5 scenario. 

Approach 2: Past population trend
Coral reef monitoring data were also applied as a proxy to estimate global level population decline. The Global Coral Reef Monitoring Network (GCRMN) compiled data related to the status and trends of coral reefs in 10 regions from 1978-2019 via the scientific monitoring observations of more than 300 network members located throughout the world. We applied the publicly available data on estimations of the percent of live hard coral cover loss at the 20%, 50% and 80% confidence intervals in the 37 subregions of the Indo-Pacific (GCRMN 2021) to estimate species population decline over the past three generations (1989-2019). The proportion of the species’ range that overlapped with each of the subregions was estimated using the Red List distribution map. The sum of the proportion of the subregional species distribution multiplied by the percent of coral cover loss in each subregion was then used to calculate the 20%, 50% and 80% estimates of coral loss across this species’ entire range.

To inform the choice of the best (i.e., lowest level of uncertainty) out of the three percentile declines, we considered 11 species-specific traits related to vulnerability to coral cover loss. Given this species’ depth range is 1-40 m and is predominately found at depths greater than 10 m, generalized abundance is considered common, overall population is not restricted or highly fragmented, does not occur off-reef, is more resilient to disease, does not recover well from bleaching or disease, has a low susceptibility to crown-of-thorns starfish, is more resilient to bleaching, has an unknown susceptibility to the impacts of ocean acidification (Kornder et al. 2018), did have >10,000 pieces exported annually in the aquarium trade between 2010-2019, it is overall inferred to be moderately susceptible to threats related to reef degradation. Therefore, past decline was suspected from the 50% percentile of estimated coral cover loss, resulting in a global level decline <25% since 1989, or over the past three generations.

This species is usually found on reef flats and reef slopes usually on soft or rubble substrates and especially in lagoons or shallow turbid environments as a free-living single polyp (Hoeksema 1990). It may reproduce asexually by budding. The maximum size is 21 cm. 

The age at first maturity of most reef-building corals is typically three to eight years (Wallace 1999). Based on this, we infer that the average age of mature individuals of this species is greater than eight years. Based on average sizes and growth rates, we also infer that the average length of one generation is 10 years. Longevity is not known, but is likely to be greater than 10 years. Therefore, any population decline rates estimated for the purposes of this Red List assessment are measured over a time period of 30 years.

This species has a relatively low susceptibility to bleaching and a low susceptibility to disease. In one study, 1% of the individuals of this species were recorded as bleached (Hoeksema 1991). In comparison to the other fungiids, this species experienced negligible bleaching in Koh Tao, Thailand during the 2010 bleaching event (Hoeksema et al. 2012). Possible species-specific adaptive mechanisms for surviving in changing climates include the capability for migration to deeper waters for refuge and the presence of a thick gastrodermis harbouring zooxanthellae (Cesar et al. 2014).

The collection of this species for the aquarium trade may lead to overharvest and localised reductions in abundance, especially for populations of naturally rare species (Bruckner and Borneman 2006). However, the wild collection of corals is highly selective and considered low impact in the long-term relative to other activities such as coral mining and dynamite fishing (Green and Shirley 1999, Pratchett et al. 2020). 

In general, the major threat to corals is global climate change, in particular, temperature extremes leading to bleaching and increased susceptibility to disease, increased severity of ENSO events and storms, and ocean acidification.

In general, the major threat to corals is global climate change, in particular, temperature extremes leading to bleaching and increased susceptibility to disease, increased severity of ENSO events and storms, and ocean acidification (Richards et al. 2008). The most recent, and first, multi-year, global bleaching event (spanning hundreds of kilometers or more) was from 2014 to 2017. Nearly 30% of reefs suffered mortality level-stress, more than 50% of affected reef areas were impacted at least twice, and some locations saw almost complete coral cover loss (Blunden et al. 2018, Vargas-Angel et al. 2019, Eakin et al. 2019). The average interval between bleaching events is now more than 50% less than before, preventing full reef recovery (Hughes et al. 2018). 

Coral disease has emerged as a serious threat to coral reefs worldwide, a major cause of reef deterioration, and may be as likely to cause mortality as bleaching in the coming decades (Weil et al. 2006, Richards et al. 2008, Maynard et al. 2015). As noted in Walton et al. (2018), in addition to thermal stress, increased coral disease prevalence and mortality can be linked to reduced water quality (Bruno et al. 2003) and clarity (van Woesik and McCaffrey 2017), nutrient enrichment (Vega Thurber et al. 2013), dredging associated sedimentation (Pollock et al. 2014, Miller et al. 2016), and plastic pollution. Based on the survey of 159 reefs in the Asia-Pacific region, the likelihood of disease increased 20-fold when corals are in contact with plastic (Lamb et al. 2018).

Localized threats to corals include fisheries, human development (industry, settlement, tourism, and transportation), changes in native species dynamics (competitors, predators, pathogens and parasites), invasive species (competitors, predators, pathogens and parasites), dynamite fishing, chemical fishing, pollution from agriculture and industry, domestic pollution, sedimentation, and human recreation and tourism activities. The severity of these combined threats to the global population of each individual species is not known (Richards et al. 2008). However, more than 60% of the world’s reefs are immediately threatened by local pressures (Bridge et al. 2013).

This species is highly traded for aquaria, with >10,000 pieces being collected from the wild and exported annually between 2010-2019 (CITES 2021). Euphyllia glabrescens is often traded as Heliofungia actiniformis because recruit morphology is similar and this makes it difficult to estimate the true level of trade (Knittweis and Wolff 2010). Although prohibited for harvest due to its rarity in Indonesia, in the past, this species has been the main target for collection in some areas and caused significant local population declines (Hadi et al. 2020). Harvest quotas should consider whether there is increased vulnerability of upstream and isolated populations and the potential for larval input from surrounding populations (Knittweis et al. 2009).

This species is classified as an Evolutionarily Distinct and Globally Endangered (EDGE) species, ranking number 41 (EDGE 2022).

All stony corals (Order: Scleractinia) are listed on CITES Appendix II, and under Annex B of the European Union Wildlife Trade Regulations. Moreover, several countries (e.g., India, Israel, Jordan, Djibouti, Fiji and the Philippines) at various stages have banned either the trade or the export of CITES II listed species, which includes all stony corals. Other countries such as Indonesia, trade maricultured corals, with quotas, production limit and regulations in place to ensure the trade is sustainable. Having timely access to national-level trade data from CITES is valuable for monitoring trends for this species. Consideration of the suitability of species for aquaria should also be included as part of fisheries management, and population surveys should be carried out to monitor the effects of harvesting alongside other population trends.